1. Field of the Invention
The present invention relates to plasma display devices, and more particularly to a surface discharge type plasma display device having an electrode configuration and a circuitry configuration which are capable of suppressing the occurrence of radiation of electromagnetic field by a plurality of high voltage pulses which form driving waveforms.
2. Prior Art
Plasma display device is one of flat display devices and an emissive type display device. And it has been expected as a display device which may realize a large-scale wall mounting TV because this plasma display may be easily manufactured using thick film technology at relatively low costs. In regard to this plasma display, discharge cells corresponding to display pixels are arranged in a matrix form to selectively discharge a discharge cell for exciting a phosphor with luminous ultraviolet rays, thereby providing three primary colors of red, green and blue. There are a DC type plasma display in which electrodes are exposed in a discharge space and an AC type plasma display in which electrodes are isolated from the discharge space. It is generally known that the AC type plasma display has a longer life time because of the isolation of electrodes from discharge space as stated above. In the AC type plasma display, there are an opposed-electrode type plasma display configured by facing electrodes to each other, and a surface discharge type plasma display having surface discharge electrodes which are configured by arranging electrodes in parallel on one substrate as disclosed in Japanese Unexamined Patent Publication No. 4-332430. Among them, the surface discharge type plasma display is generally considered to be the most suitable for large scale color display because it has a wide memory margin, high brightness and emissive efficiency.
FIG. 4 shows a block diagram of a system configuration of a conventional surface discharge type plasma display device. This display device is similar to the surface discharge type plasma display shown in the article titled xe2x80x9cDriving method of 40-inch type full-color ACPDPxe2x80x9d in the Japanese monthly magazine xe2x80x9cMonthly Displayxe2x80x9d (pp. 46-50, April, 1996).
According to a block diagram of a drive unit, this conventional surface discharge type plasma display comprises a plasma display panel 15, a data driver 16, a sustaining driver 17, a scanning driver 18, a scanning pulse generator circuit 19 and a mixer 20.
Display data and control signal from outside of the device are appropriately converted by an interface circuit, and supplied to a data driver 16, a sustaining driver 17 and a scanning driver 18 (the interface circuit is not shown in the block diagram).
FIG. 5 shows a schematic cross sectional view as an example of one pixel of a surface discharge type plasma display panel used in the above device. The panel comprises an insulative substrates 1, 2, a transparent scanning electrode 3, a transparent sustaining electrode 4, trace electrodes 5, 6, a data electrode 7, a dielectric layers 12, 14, a protective layer 13, a phosphor 11 and a plurality of ribs 9. A numeral 8 designates a discharge gas space. In the figure, though the ribs 9 are not depicted in detail, the striped ribs are formed to be transverse with the scanning electrode 3 and sustaining electrode 4 to separate pixels and keep the space between insulative substrates 1 and 2. Furthermore, metal electrodes (trace electrodes 6, 7) are laminated on both of the scanning electrode 3 and the sustaining electrode 4 to decrease the resistance thereof.
FIG. 6 shows schematic views of driving pulse trains of said surface discharge type plasma display panel. On the scanning electrodes 3 corresponding to the rows of matrix displays, pulse trains SC1, SC2, SC3, SCn (xe2x80x9cnxe2x80x9d is an integer in response to the number of lines) are applied in the order from the above. Pre-discharge pulses or priming pulses, scanning pulses, sustaining pulses B of the pulse train (SCn) to be applied to the scanning electrode 3 are generated by a high voltage pulse generator 19 for the scanning electrodes 3, and its timings are controlled by the signal of interface with a scanning driver 18. The sustaining electrodes 4 paired with scanning electrodes 3 are connected in common and a sustaining pulse trains SUS are applied thereto. The priming pulse and the sustaining pulse A of the pulse train (SUS) to be applied to the sustaining electrodes 4 are generated by a high voltage pulse generator 17 for the sustaining electrodes 4. Since the priming pulses and the sustaining discharge pulses A, B are applied at the same time to all scanning electrodes 3 and to all sustaining electrodes 4, it is required that withstand voltage is high, voltage is large and ON-resistance is low. Thus, a circuit is configured with discrete parts such as FETs and resistors. On the other hand, scanning pulses (Vw) are applied to the scanning electrodes 3 respectively at different timings, and accordingly, the number of circuits should be the same as that of the scanning electrodes 3. Therefore, IC with high withstand voltage is used to superimpose scanning pulses by using diode circuit in a mixer 20 and apply them to the scanning electrodes 3. Furthermore, IC with high withstand voltage is used because data electrodes 7 need to be applied data pulses independently according to the display data.
The reason for using ICs with high withstand voltage is that since the scanning electrodes 3 and the data electrodes 7 are driven independently, a lot of circuits are required, and since output electric current is relatively small, integration is enabled and the drive circuit may be cost down.
The driving pulse trains SUS, SCn and DATA are divided respectively into a pre-discharge (priming) period Tp, write-in discharge (addressing) period Tw and sustaining discharge period Ts, respectively. The priming period Tp applies priming pulses between the scanning electrodes 3 and the sustaining electrodes 4 to generate discharge and to crease charged particles and excitation particles such as ions and electrons as well as to control wall charges on the scanning electrodes 3, sustaining electrodes 4 and data electrodes 7 with fixed amounts, thereby serving to stabilize the discharge of the addressing period Tw.
During the priming period Tp, all scanning electrodes 3 are applied with the scanning pulses successively, and write-in discharges are generated, in relation with the data electrodes 7, by means of data pulse to be applied in accordance with the display data, thereby serving to address the display data as the wall charges.
During the sustaining discharge period Ts, the sustaining pulses A shown in FIG. 6 are applied to the scanning electrodes 3 while the sustaining pulses B shown in FIG. 6 are applied to the sustaining electrodes 4, thereby sustaining the display discharge. Thus, the write-in discharge is created only in the pixel issuing luminescence according to the display data between the scanning electrodes 3 and the data electrodes 7 so as to form the wall charges on the protective layer 13 on the side of the scanning electrodes 3. Based on this information, the discharge is sustained between the scanning electrodes 3 and the sustaining electrodes 4 to obtain desired luminescence. The display is performed by exciting selectively the red, green and blue phosphors 11 by ultraviolet rays created by the sustaining discharge.
Since surface discharge type plasma display panel uses the ultraviolet rays generated by discharging as mentioned above, it requires high voltage pulse trains of such frequency of several hundred kHz having a value of wave height of around several hundred voltages, and further it requires relatively high power. In the sustaining discharge period, therefore, the sustaining pulses B are applied to the scanning electrodes 3 as shown in FIG. 6, while the sustaining pulses A is applied to the sustaining electrodes 4. Since the sustaining pulses A and B are applied to all scaning electrodes 3 and to all sustaining electrodes 4, currents for charging and discharging the capacity between both electrodes become large impulse currents, and flow in the drive circuits, the scanning electrodes and the sustaining electrodes at the same time and in the same directions. This impulse current becomes not less than 10 times of impulse current generated at times of the write-in discharging or other discharging, and is a main cause of unnecessary radiation of the electromagnetic field in the surface discharge type plasma display.
For example, when displaying a whole surface of a large sized panel of 33-inches or 42-inches types with high brightness, the impulse current of several amperes at maximum flows, whereby there occurs disadvantage that a fairly strong unnecessary radiation of the electro-magnetic field is caused from the scanning electrodes, sustaining electrodes, high voltage drive circuits and others.
FIG. 7 schematically shows, taking out from the block diagram of the system configuration of FIG. 4, the connections between the high voltage pulse generator 19 for the scanning electrodes and the high voltage pulse generator 17 for the sustaining electrodes during the sustaining discharge period as-well as the scanning electrodes 3 and the sustaining electrodes 4 and directions of main impulse currents.
When displaying, the sustaining pulses B are applied to all scanning electrodes 3 from the high voltage pulse generator 19 and the sustaining pulses A are applied to all sustaining electrodes 4 from the high voltage pulse generator 17.
These sustaining pulses A and B have rectangular waves of about 200 V having frequencies of several hundred kHz of reversing the phases each other. Accordingly, the impulse current flows along a current path I1 at rising and falling of the sustaining pulses A and B from the high voltage pulse generator 19 through the scanning electrodes 3 and sustaining electrodes 4 to the high voltage pulse generator 17 (the current path is designated with xe2x80x9cI1xe2x80x9d of FIG. 7), and at subsequent falling and rising, an impulse current of opposite directions flows. Thus, this is repeated alternately.
Therefore, for displaying the whole of the faceplate, all discharge spaces should be discharge so that the impulse current flows in all scanning electrodes 3 and sustaining electrodes 4, and current value increases, and correspondingly unnecessary radiation of electromagnetic field increases. Further, since this impulse current is large, it invades as voltage or current noises into the drive circuits, and disturbs image signals and hinders pictures.
A method of avoiding unnecessary radiation of electromagnetic field and invasion of noises into pictures is disclosed in Japanese Unexamined Patent Publication No. 7-248744, in which the sustaining pulse is phase-modulated by a pseudo-random noise generating circuit and applied. This driving method disperses the impulse current generated by discharging when displaying, thereby decreasing the peak value of the current so as to check occurrence of unnecessary radiation of electromagnetic field and noises.
On the other hand, for a method of suppressing unnecessary radiation of the electromagnetic field, as disclosed in Japanese Unexamined Utility Model Publication No. 59-63956, such a configuration is proposed that a transparent shielding film filter is arranged on the surface of plasma display panel. Although this shielding technique suppresses unnecessary radiation of electromagnetic field, the shielding effect of the electromagnetic field is not sufficient. A more effective alternative is to use a good conductor or a mesh filter plated with the good conductor.
According to the method of dispersing the discharged impulse current, since the discharging timing should be phase-modulated at random, disadvantageously the driving circuit is complicated, and the driving margin is narrowed.
On the other hand, the method of arranging the shielding film of the electromagnetic field is to suppress unnecessary radiation of electromagnetic field by enclosing it, perfect shielding effect of the unnecessary radiation of electromagnetic field could hardly provided in itself. For increasing the realizing effect, as an implementation effect, the good conductor is used or a resin plated with the good conductor is used for a frame and they are should be grounded.
The stronger the unnecessary radiation of the electromagnetic field from the plasma display is, the higher the costs for preventing radiation of the electro-magnetic field become. Further, the larger the display planed is, the higher the costs for suppressing radiation of the electromagnetic field become, since said pmpulse current increases.
It is an object of the present invention to provide an arrangement of electrodes and a wiring configuration of drive circuits which may decrease unnecessary radiation of electromagnetic field with respect to a surface discharge type plasma display, without resorting to additional electromagnetic shielding filter or a frame, and thus plasma display may be realized at low costs.
According to the present invention, adjacent surface discharge electrodes are driven so as to have opposite discharge directions to each other. Preferably, the discharge directions are determined so as to suppress the radiation of unnecessary electromagnetic field.
Furthermore, all of the surface discharge electrodes are divided into a plurality of blocks, and which are arranged such that its discharge currents are turned in opposite one another with respect to adjacent blocks.
Furthermore, the current flowing directions of wiring of the drive circuits of the surface discharge electrodes and circuit group are configured to be in opposite direction with respect to at least one wiring and circuit of the drive circuits of the at least surface discharge electrodes.
Preferably, the current flowing direction of the wiring group of the surface discharge electrodes and the circuit group are arranged to be opposite alternately.
The wiring group and circuit group of the drive circuits of the surface discharge electrodes are divided into at least one drive circuit block, and the drive circuits of the surface discharge electrodes are configured such that the currents of the drive circuit group are in opposite directions with respect to at least one drive circuit block.
More preferably, the color plasma display has the same number of the wiring group and the circuit group of the drive circuits of the surface discharge electrodes of the currents facing in opposite directions, and comprises the drive circuits of the surface discharge electrodes of the same number as the drive circuit blocks of the surface discharge electrodes, and has the same number as the drive circuit block of the surface discharge electrodes of the current facing in opposite directions.